It is very often desired to utilize a lamp at a less than maximum intensity. For this purpose, typically dimmers are installed in the circuit supplying the electric power to such lamps.
Most dimmers operate on a basis of chopping the power, meaning, transmitting only through part of the time of the alternating current cycle, shutting it off during the rest. The extent of the transmission time in each cycle determines the amount of dimming.
Dimmers typically consist of a user-controlled potentiometer operating in conjunction with a triac or an SCR.
Most available dimmers, particularly such as available in domestic use, are capable of dimming a light of lamps such as incandescent type lamps or halogen lamps. However, standard dimmers are unsuitable for dimming light of gas discharge lamps such as fluorescent lamps, high or low pressure mercury or sodium lamps, etc. When attempting to dim such lamps by conventional dimmers that are used for example, for incandescent or halogen lamps, the light of a gas discharge lamp either flickers or extinguishes altogether.
There is a long felt need for dimmers suitable for use with gas discharge lamps particularly in view of the popularity of such types of lamps. As is no doubt is known to the artisan, the popularity of such lamps stems to a large extent from their very high efficiency, meaning the very high ratio of illumination intensity to power consumption.
Gas discharge lamps have a gas filled space or tube with two spaced electrodes (heated or not). When heated, an electrode is a two terminal filament. One terminal of each of the two electrodes is connected to a pole of the AC power source and the other terminals of the two electrodes are typically linked together by the intermediary of a so-called "starter".
A choke/ballast is installed between one of the electrodes and the respective pole of the power source and sometimes a capacitor is installed in series or parallel to the lamp to correct the power factor (cos-fi) and/or limit the current.
In order to initiate an electric discharge through the gas, an initial high voltage, that can supply enough electric charge is required. When the power is turned on, an appropriate voltage is to be generated to cause such a discharge.
For a fluorescent lamp, that has heated electrodes, the electric current flows at first, through the choke, one filament electrode of the starter and the second filament electrode of the lamp. After an initial short period of time, the filaments are hot and the starter disconnects, with the result of abrupt current change through the choke which, in turn, causes a very high voltage across the fluorescent lamp, above the threshold required for ignition of the discharge. Following initial ignition, the gas discharge lamp continues to emit light while the choke limits the current, as long as it is supplied with electric power above a minimal value.
There are available dimmers for gas discharge lamps such as fluorescent lamps. For example, in Hi-Fi dimmers, the standard choke is replaced by an electronic choke which is an oscillator that generates an alternating electric power at high frequency, of the order of 25-100 KHz. In such dimmers, dimming is achieved by modulating the oscillator and whilst effective dimming is achieved, such dimmers entail significant drawbacks in that they are somewhat inefficient and expensive and that retrofitting a light circuit to operate them requires relatively expensive hardware.
Other types of dimmers involve the use of a heating transformer intended to preheat the filaments in order to reduce the threshold voltage required to initiate the gas discharge.
The drawback here is similar to that of the Hi-Fi dimmers in that it requires a very expensive hardware. Furthermore, such dimmers are inappropriate for various kinds of gas discharge lamps that do not depend on preheating of their electrodes such as various types of high pressure gas discharge lamps and high or low pressure mercury or sodium lamps and others.
It is the object of the present invention to provide a novel dimmer for gas discharge lamps.
It is furthermore the object of the invention to provide a dimmer which can easily be installed in already existing installation of gas discharge lamps.
It is furthermore the object of the present invention to provide such dimmers involving the use of inexpensive hardware.